A wide variety of heat exchangers exist in the chemical, food, beverage, dairy, and pharmaceutical industries for cooling or heating various liquids. In a typical heat exchanger, heat energy is transferred between two fluids. A barrier separates the two fluids. The barrier may be a gasketed plate, a pipe, or a jacket. The barrier must maintain integrity and separate a product side chamber and a media side chamber. Leaks are undesirable and often dangerous.
Existing heat exchanger designs often employ a tube within a tube design, a tube bundle with multiple tubes attached to a tube sheet that is set in a shell, a spiral tube in a shell, or a design that uses multiple gasketed plates in a frame.
The basic concept of the plate and frame type heat exchanger is to pump fluids on either side of a thin metal plate so that heat may be transferred between the two fluids, e.g. the product and the media.
In all cases the integrity of the barrier and of the gasket material must be maintained.
As the heat exchangers are operated corrosion, erosion, thermal stress and gasket elastomer degradation result in leakage between the product chamber and media chamber. When leakage occurs during operation, a transfer of fluid from one chamber to the other occurs.
Often leaks become apparent only after the product has leaked into the media, or media into the product. If the latter occurs, it is likely that the adulterated product will be considered damaged. In some processes, such as those present in the food, beverage and dairy industries, contamination of this sort may have severe consequences. Heath risks may occur from contaminated products after the media flows into the product.
Needs exist for testing methods for heat exchangers that detect leaks before product or media becomes contaminated.
Current predictive measures usually involve disassembly for visual inspection and dye checking for holes or penetrations of any sort. Dye testing is a means of locating the position of the penetration, sometimes as small as a pinhole. This is generally done as part of routine maintenance procedure. Plates determined to be defective are discarded, and replacements are installed in the plate pack. Re-gasketing is usually done during these routine maintenance procedures.
There are two other common methods used to predict leaks without disassembly. One involves pressurizing one chamber with air and monitoring pressure loss. This method may work for large leaks, but is not practical for small leak determination.
Another method, used for small leak detection, uses a difference in conductivity between solutions that are pumped on each side of a heat transfer surface barrier. Analytical equipment detects conductivity increases in the low conductivity solution if a leak path exists. This method is costly to employ, and is far more complex than a mass flow rate detection method of testing.
Needs exist for methods of detecting leaks in heat exchangers that are inexpensive and do not require disassembly of the heat exchanger unit.